missed function implemented

Author: bmorcelli

src/core/display.cpp

@@ -1869,6 +1869,10 @@ bool preparePngBin(FS &fs, String filename) {
     return ok;
 }
 #else
+bool preparePngBin(FS &fs, String filename) {
+    log_w("PNG: Not supported in this version");
+    return true;
+}
 bool drawPNG(FS &fs, String filename, int x, int y, bool center) {
     log_w("PNG: Not supported in this version");
     return false;